It is known that polymers having a phosphorylcholine-like group have excellent biocompatibility such as inactivatability of blood constituents or non-adsorbability of biomaterials, attributed to its phospholipid-like structure originated from biomembrane, and are superior in properties such as antifouling and moisturizing properties. Active research and development have been made for synthesis and use of the polymers having a phosphorylcholine-like group, aiming at development of biomaterials which make good use of such properties, and some investigations have been made of hydrogels containing the polymers having a phosphorylcholine-like group.
For example, it is reported that a hydrogel film has been obtained by dissolving in an ethanol solution a copolymer of a monomer having a hydrophobic functional group and a monomer having a phosphorylcholine-like group, applying the resulting mixture over a substrate, evaporating the ethanol by solvent evaporation to prepare a film, and swelling the film in water (K. Ishihara et al., Japanese Journal of Polymer Science and Technology, 46, P591 (1989)).
With this copolymer for hydrogel films, however, a gel cannot be prepared directly from the copolymer solution, since the preparation of a gel requires formation of a polymer film having a cross-linked structure, followed by swelling in water. The cross-linked hydrogel films thus obtained are substantially insoluble in water at an ordinary temperature.
A method is also reported for preparing a hydrogel that may be used for contact lenses, including mixing and cross-linking a monomer having a phosphorylcholine-like group and a cross-linking monomer (JP-5-107511-A, JP-9-20814-A).
This hydrogel is in the form of a chemically cross-linked clot, and is substantially insoluble in water at an ordinary temperature.
Another method for preparing hydrogel films is also reported, including forming a polyion complex from a polymer having a phosphorylcholine-like group with an anionic functional group and that with a cationic functional group (K. Ishihara et al., J. Biomedical Materials Research, 28., p1347, 1994).
The polyion complex for preparing the hydrogel films cannot substantially be dissolved in water at an ordinary temperature, since each polymer strongly coagulates in an aqueous solution.